Sensitivity or specificity of reverse transcriptase-polymerase chain reaction assays: the real challenge for molecular staging of prostatic carcinomas

Numeric definition of the clinical performance of the nested reverse transcription-PCR for detection of hematogenous epithelial cells and correction for specific mRNA of non-target cell origin as evaluated for prostate cancer cells

BACKGROUND

Inappropriate quality management of reverse transcription-PCR (RT-PCR) assays for the detection of blood-borne prostate cancer (PCa) cells hampers clinical conclusions. Improvement of the RT-PCR methodology for prostate-specific antigen (PSA) mRNA should focus on an appropriate numeric definition of the performance of the assay and correction for PSA mRNA that is not associated with PCa cells.

METHODS AND RESULTS

Repeated (RT-)PCR tests for PSA mRNA in single blood specimens from PCa patients and PCa-free controls, performed by four international institutions, showed a large percentage (approximately equal to 50%) of divergent test results. The best estimates of the mean, lambda (SD), of the expected Poisson frequency distributions of the number of positive tests among five replicate assays of samples from PCa-free individuals were 1.0 (0.2) for 2 x 35 PCR cycles and 0.2 (0.1) for 2 x 25 PCR cycles. Assessment of the numeric value of the mean can be considered as a new indicator of the performance of a RT-PCR assay for PSA mRNA under clinical conditions. Moreover, it determines the required number of positive test repetitions to differentiate between true and false positives for circulating prostate cells. At a predefined diagnostic specificity of > or = 98%, repeated PCRs with lambda of either 1.0 or 0.2 require, respectively, more than three or more than one positive tests to support the conclusion that PSA mRNA-containing cells are present.

CONCLUSIONS

Repeated nested PCR tests for PSA and appropriate handling of the data allow numeric quantification of the performance of the assay and differentiation between analytical false and true positives at a predefined accuracy. This new approach may contribute to introduction of PSA RT-PCR assays in clinical practice.

Prognostic value of circulating prostate cells in patients with a rising PSA after radical prostatectomy

BACKGROUND

To predict poor outcome in patients with a biochemical recurrence (rising PSA) after radical prostatectomy (RP), urologists rely primarily on Gleason score, PSA doubling time, and time from surgery to biochemical (i.e., PSA) recurrence. In the present study, we assess the value of RT-PCR detection circulating prostate cells in blood of patients with a rising PSA.

METHODS

RNA from blood samples was obtained from 55 patients with a rising PSA and from 45 patients without evidence of biochemical failure (PSA < 0.1 ng/ml). Both groups were matched for age, Gleason score, pT stage, and interval between radical prostatectomy and PCR testing.

RESULTS

PSA positive cells were detected in 1/45 (2%) patients without a PSA recurrence and 19/55 (34%) patients with a PSA recurrence. In the rising PSA group, mean PSA doubling time was significantly shorter in patients with positive RT-PCR (5 months) than in patients with negative RT-PCR (16 months; P = 0.001). An earlier onset of recurrence was also detected in patients with a positive RT-PCR (31 months for positive RT-PCR vs. 50 months for negative RT-PCR) but this result did not achieve statistical significance (P = 0.102). Salvage radiation therapy was administered in 15 patients. Three of the five patients with a positive RT-PCR progressed during radiotherapy whereas 7 of the 10 patients with a negative RT-PCR obtained a complete response and none have progressed.

CONCLUSIONS

These preliminary results suggest that RT-PCR detection of prostate cells in blood of patients after RP correlates with rapidly progressing biochemical failure after RP.

Carcinoembryonic gene member 2 mRNA expression as a marker to detect circulating enterocytes in the blood of colorectal cancer patients

BACKGROUND

The aim of this study was to report our experience with a new molecular tool to detect circulating enterocytes in the blood of patients with colorectal cancer.

METHODS

The study included 193 individuals: 78 patients with colorectal cancer and 115 controls composed of patients with benign colorectal diseases (n = 16), patients with noncolorectal cancer (n = 31), healthy individuals (n = 62), and healthy bone marrow transplantation donors (n = 6). A nested reverse transcriptase-polymerase chain reaction with specific primers for the carcinoembryonic gene member 2 (CGM2) was used to detect circulating enterocytes in the peripheral blood of 78 patients with colorectal cancer. The blood (n = 109) or the bone marrow (n = 6) of the 115 controls was studied to test the absence of CGM2 illegitimate transcription in nucleated blood cells and nucleated blood cell progenitors. The assay sensitivity was effective in detecting 1 CGM2-positive cell per 10(6) nucleated blood cells.

RESULTS

Fifty-nine percent (46/78) of patients with colorectal cancer were found positive whereas all negative controls remained negative. Positivity rates were 38% (3/8) in Dukes' A classification, 43% (9/21) in Dukes' B, 77% (23/30) in Dukes' C, and 58% (11/19) in Dukes' D.

CONCLUSIONS

The clinical significance of enterocyte detection in the blood of colorectal cancer patients by means of this CGM2 messenger RNA assay needs further evaluation.